A standard heavy-duty shear for cutting profiled steel rods and like workpieces has a frame supporting a stationary main blade, a movable blade displaceable adjacent the main blade, a main holddown which presses the workpiece down against the main blade prior to and during the cut, and a cut-off holder which presses the cut-off end of the workpiece up against the movable blade during the cut. The cut-off holder serves to maintain the piece being cut off in accurate position before and as it is sheared off the workpiece.
In German patent document 1,815,691 filed Dec. 19, 1968 by Joachim Wepner such a system is disclosed where the cut-off holder presses the workpiece fairly solidly back in the cutting direction against the movable blade. Thus not only must the movable blade be pushed forward with a force sufficient to shear the workpiece, but this force must additionally be able to overcome the opposite force of the cut-off holder. Typically pressure in a cylinder pushing the cut-off holder against the workpiece is established by an overpressure valve so that as the cut-off holder is forced down by the movable blade, this valve is forced open by back pressure to relieve the extra pressure created in the holder cylinder.
The main disadvantage of this system is that the main cylinder that pushes the movable blade down (it being noted that the terms "down" and "up" are used here purely for convenience and that the system would work perfectly well if inverted or on its side) must work not only against the workpiece, but against the cut-off holder. The fluid pumped into and out of the holddown cylinder does no meaningful work, but still the system must move and cool this fluid and provide sufficient pressure to the main cylinder for it to do its double job. The result is therefore a fairly complex system that is more costly to operate than the work it does would seem to warrant.